Mind the Gap: When third party services are not enough to achieve security or compliance to PCI DSS

MasterCard published a very brief document outlining the very popular Use Case where a Merchant leverages a third party e-commerce system for processing transactions by redirecting to a separate hosted site. The attraction is the obvious shift of the payment card environment to that of the hosted page provider. This does help in reducing the PCI DSS scope, but as highlighted within the paper “…does not remove the need for a robust information security program.”

The brief highlights there is a risk to Merchants (“Based on the current compromise and attack trends”) where attackers may attack the Merchant’s web environment to redirect the traffic from the approved Hosted-Page vendor to a malicious party site. This can be executed with a fake page where nothing but an error occurs, or the attackers can proxy (pass through) the traffic to the true Host-Page vendor. This second approach allows the transaction to occur without any notice to the user of the attack.

The attack mitigation presented (follow best practices) are expected. It does not say to solely or specifically to follow PCI DSS specifications, but instead to follow best practices appropriate for the web environment itself.

An additional attack mitigation stated is to establish SSL tunnels to fixed addresses and certificates. This is definitely effective when securing the point to point connection, but generally would be ineffective from the attack described (as an attacker could simply compromise from the Merchant Host itself).

An alternative mitigation approach to consider would be expanding the monitoring & response capabilities. As an example, if traffic is being redirected and the host Merchant server is compromised than the next best technique would be (among many) to have automatic triggers at the IPS, FW, and ACL points when these hosts are transmitting to unapproved targets. This highlights the important need of when procuring services with valuable data, to have a deep process of onboarding the Service Provider in a manner that brings to light these technical details and establishes operational response capabilities jointly with the vendor.

The article is short and worth a read. A key question that rang throughout the article was – does the issuance of this guidance make it clear that if the Use Case Attack happens than Y Merchant is deemed out of PCI DSS compliance? The closing paragraph provides some light. Would love others thoughts here too!

“While a merchant may be able to reduce or remove the scope of its environment’s applicability to comply with PCI DSS requirements by using hosted payment pages, it does not remove the merchant’s risk of being involved in, or even the source of, an account data compromise event.

Merchants still have a duty to employ security controls based on industry best practices to their web based environment to protect payment card data.”